TVSS filters have been available for decades and are not only stand alone power protection devices but are often incorporated into other power protection devices such as voltage regulators and uninterruptable power supplies. The Institute of Electrical and Electronic Engineers (IEEE) has published numerous studies that indicate transients (also called spikes or surges) and noise (also called high frequency low magnitude interference) related problems are the most frequent power disturbance problems. These power disturbances have become more significant as microprocessor use has rapidly expanded. Microprocessors are also becoming more susceptible to transients and noise, causing equipment damage, logic control errors and expensive downtime.
There are many types of TVSS filter solutions. The basic circuit components consist of some combination of the following:
1. Clipping Devices, which are activated by voltage above a certain level and react to voltage only above the level. Typical components include: PA1 2. Crowbar devices, which are activated by voltage above certain levels and short the power line until the incoming voltage is lowered to a predetermined level. Typical components include: PA1 3. Electrical noise filter components, which are energy storage devices that react to frequency changes. Typical components include: PA1 improved power protection performance typically measured as lower let through voltage; PA1 greater durability and longer life for the invention and protected equipment; PA1 lower cost; PA1 smaller size; and PA1 simplicity to manufacture. PA1 1. Diodes which convert AC to DC power and trigger levels set as low as 0.7 volts above the peak AC voltage. When a surge or over voltage exceed this trigger level, the diode converts the energy above this level to DC voltage. As the diodes are in a FWB circuit either positive or negative surges will be converted. PA1 2. DC capacitor which absorbs the positive DC electricity converted by the diodes and stores the excess energy. DC capacitors are a much smaller size and have a lower cost compared to comparable AC capacitors, allowing for much greater energy storage. The capacitor, once charged above its trigger level, will discharge the stored energy as positive DC electricity, which must flow through the resistor, as the diodes are uni-directional. PA1 3. The resistor dissipates the DC power which is discharged by the DC capacitor. No electrical energy is released back to the system. Proper sizing of resistors allows for controlled dissipation of energy to the typical charged state of the capacitor which is just above the peak system voltage.
metal oxide varistor (MOV) PA2 diode or transorb or avalanche diode or zener diode PA2 spark gap PA2 gas tubes PA2 thyristor (SCR) PA2 AC capacitors PA2 inductors or chokes or coils PA2 Patents for TVSS filter circuits include: U.S. Pat. Nos. 4,912,589; 4,628,394; 4,563,720; 4,068,279; 3,793,535 and Canadian Patent No. 1,332,074.
These components can be arranged in a infinite number of circuits creating effective TVSS and TVSS filters. Many circuits have been used for a number of years and a large body of prior art exists such as prior products, electrical engineering teachings and electrical association recommendations.
There are many locations where TVSS filter circuits can be applied within a facility. The most common location uses a TVSS device between a wall receptacle and the load to be protected. Another location is within the application or load itself, although the circuits utilized at this location often just contain MOVs. A third location is for a TVSS filter circuit to be attached or designed within the electrical distribution equipment of a facility. This equipment includes circuit breakers, meter panels, panel boards, switch boards, switch gear and motor control centres. The invention can be located in any of the above locations but is most economical when applied in the electrical distribution equipment.
Prior art electrical power protection circuits have dramatically improved with the use of clipping components (especially MOVs) and AC capacitors. MOVs are able to repeatably shunt large transients and are activated by voltage above a certain level. Their limitation is the voltage level at which the MOV begins to react. For a 120 VAC system the nominal peak voltage is 172 VDC. The system VAC can be as high as 127 VAC with a peak voltage of 180 VDC. Hence the MOV cannot begin operations below 180 VDC, at it would quickly deteriorate. The level at which the MOV begins operation is called the maximum continuous operating voltage (MCOV) and the lower it is set, the lower the let through voltage. Let through voltage is the remaining voltage of a transient after being reduced by a power protection device. The problem with setting a lower MCOV for MOVs is that it can dramatically reduce the life of the MOV. To maximize lifetime, 200% or greater MCOV compared to peak voltage (VAC peak=1.414.times.Vrms) has a very long life and survives the possible problem of continuous over voltage caused by mis-wiring within the electrical system.
Below 115% of peak voltage, a clipping device is very susceptible to utility surges and transients which substantially shorten the component's life. At 115% to 200% a clipping device can be damaged by continuous over voltage and extreme surges while having a reasonable life in a standard environment.
AC capacitors react to voltage frequency changes and hence absorb high frequency electrical noise and small transients. AC capacitors however, release energy back relatively slowly to the system allowing them to be overwhelmed by continuous and severe high frequency electrical noise and harmonics. For higher voltages such as 208, 480, and 600 volt systems, the size and cost of effective AC capacitors can become prohibitive.
The combined use of MOVs and AC capacitors provides a range of protection, from small transients and high frequency electrical noise, to large surges. The combined use also provides current sharing where each component absorbs or shunts a portion of a transient's energy which extends the life of all components. This current sharing is limited by the cost and size constraints of AC capacitors and the MCOV of MOVs. What is required, however, and what the present invention intends to provide, is a component or circuit that can be set near to the peak voltage level to be encountered from the utility and absorb or shunt transients ranging to above 200% of this peak voltage. This would allow much better sizing of AC capacitors as the effect of current sharing, from this invention, would help protect them from continuous electrical noise and harmonics. MOVs could also be set at a higher MCOV, dramatically increasing their life.
Many different arrangements using clipping, crowbar and electrical noise filter devices have been proposed to achieve greater durability and lower the let through voltage. The general result has been greater current sharing through a greater number of components. The present invention has taken a very different approach of using direct current (DC) components within a circuit that achieves low MCOV, long life, and robust current sharing in the 100% to 200% range of peak voltage. When combined with clipping devices and AC capacitors, the total of all devices provides much lower let through voltage and greater durability.
The invention is similar to an AC to DC power supply used in many typical electrical and electronic products. The foremost common power supply circuits are the halfway rectifier (HWR) which is able to handle either positive or negative surges, but not both, the full-wave center tap (FWCT), the dual complimentary rectifier (DCR), these latter two both requiting a center tap transformer while the DCR also requires grounding, significantly reducing the configurations these latter two circuits can be applied to for power protection purposes, and the full-wave bridge (FWB). When altered for power protection, the FWB is able to handle both positive and negative electrical disturbances and work on all electrical configurations. To be utilized for power protection however, such circuits would need to be substantially altered.
While the inventor is not aware of any commercial use of an adaption of the FWB for power protection, three existing patents are known which teach the use of diodes.
U.S. Pat. No. 4,321,644 issued Mar. 23, 1982 does not relate to the invention but the prior art in the patent does. This prior art applies diodes but in a very complex manner with non-disclosed trigger signal devices controlling the diodes. The capacitor appears to be an AC capacitor. The use of an AC capacitor within the circuit would have a zero charge causing a large initial current draw, high recovery time, and rebound effects. The invention has none of these restrictions or the complexity of the circuit.
Canadian Patent No. 1,230,919 dated Dec. 29, 1987 uses DC capacitors but has no resistor and uses Zener diodes. The circuit is designed as a cascade where the DC capacitors handle smaller surges while the Zener diodes activate for large surges. The circuits send transients to ground, unlike the invention, which absorbs transients and then dissipates the energy by utilizing a resistor.
U.S. Pat. Nos. 4,870,528 and 4,870,534 dated Sep. 26, 1989 are replicated in Canadian Patents Nos. 1,332,439 and 1,333,191. We will only deal with U.S. Pat. No. 4,870,534 as it is more generic in nature while U.S. Pat. No. 4,870,528 is a three wire detailed adaptation of U.S. Pat. No. 4,870,534. The patent utilizes the invention circuit for power protection use in a much different manner. Rather than combine the circuit in parallel with MOVs or AC capacitors, the patent goes to lengths to discredit these components for power protection use. Instead the patent relies on a two tiered approach with each tier containing a coil or inductor and then the adoption of the FWB circuit. These two patents limit the circuit's use to series circuits of only one phase. The invention, instead, utilizes parallel circuits with clipping devices (MOVs, Avalanche diodes, Zener diodes) and/or AC capacitors. This dramatically expands the operating amperage range the invention can be utilized for. Series products meanwhile must be accurately sized for their application. Multiple phases with ground and/or neutral configurations can also be utilized with the invention. The LED indicator in the circuit is also not included in the invention's circuit. The parallel nature of the invention circuit allows a signal to be monitored at a sensor board on the device, if monitoring is required.